1. Field of the Invention
The present invention relates to a dielectric porcelain composition for high frequency waves, used in a high frequency band of e. g., microwaves or millimeter waves, particularly, to a dielectric porcelain composition useful as a material for circuit boards of microwave integrated circuits, millimeter waves integrated circuits and the like, dielectric strips and dielectric antennas used in a microwave band and a millimeter wave band, and to a dielectric resonator and nonradiative dielectric strip using the same.
2. Description of the Related Art
There have been cases in high frequency circuits such as microwave integrated circuits and millimeter wave integrated circuits that such a structure is employed that a dielectric porcelain for resonance is fixed on a dielectric board through a dielectric supporting member.
FIG. 1 is a cross sectional view showing a constitutional example of a dielectric resonator. That is an example of a dielectric resonator applied to a dielectric resonator control type microwave oscillator, constituted such that a dielectric porcelain 1 is attached to a dielectric board 3 through a dielectric supporting member 2 and is electromagnetically coupled to a strip line 4 formed on the dielectric board 3 by utilizing an electromagnetic field H which leaks outside the dielectric porcelain 1, which are housed in a metallic container 5.
Since a resonance system of high unloaded Q level can be constituted in the high frequency circuit by controlling the leakage of electric field of the dielectric porcelain 1 through the dielectric supporting member 2, it is necessary to use, for the dielectric supporting member 2, a material having a low dielectric constant and a small dielectric loss (tanxcex4), i.e., a large Q value. Therefore, forsterite (2MgOxc2x7SiO2) ceramics having a dielectric constant of about 7 and a Q value at a measuring frequency of 10 GHz of about 15,000 has been used as the material for the dielectric supporting member 2, and alumina ceramics having a dielectric constant of about 10 and a Q value at a measuring frequency of 10 GHz of about 20,000 or more has been mainly used as the material for the dielectric board 3.
Cordierite (2MgOxc2x72Al2O3xc2x75SiO2) ceramics has been known as a dielectric material having a low dielectric constant. Since a dense sintered body of the cordierite ceramics is difficult to obtain owing to its remarkably narrow sintering temperature range, glass ceramics has been known that is obtained by adding a glass material to result a dielectric constant of from 4 to 6 and a Q value at a measuring frequency of 10 GHz of about 1,000.
Furthermore, there has been known a nonradiative dielectric guide (hereinafter referred to as an NRD guide) having a guide for transmitting a high frequency signal comprising a dielectric material.
FIG. 2 is a partially cutaway perspective view showing a basic constitution of an NRD guide of the invention and the conventional art. An NRD guide S1 comprises a dielectric strip 12 intervening between a pair of parallel flat conductive bodies 11 and 13 having a distance of xcex/2 or less, in which xcex is the wavelength of a high frequency signal (electromagnetic wave), such as a millimeter wave, propagating in the dielectric strip 12. In the NRD guide S1, the electromagnetic wave is shielded and cannot enter from the outside when the distance of the parallel flat conductive bodies 11 and 13 is xc2xd or less of the wavelength xcex of the high frequency signal, but when the dielectric strip 12 is made intervene between the parallel flat conductive bodies 11 and 13, the electromagnetic wave can propagate along the dielectric strip 12 inside the same, and a radiation wave is suppressed by the shielding effect of the parallel flat conductive bodies 11 and 13. In FIG. 2, a part of the upper parallel flat conductive body 13 is cut for viewing the interior. The wavelength xcex of the high frequency signal is that at the use frequency in the air.
The electromagnetic wave propagation mode of the NRD guide S1 includes two modes, i.e., the LSM (longitudinal section magnetic) mode and the LSE (longitudinal section electric) mode, and the LSM mode that exhibits a small loss is generally employed.
A curved dielectric strip 12 can also be used, and in this case, since an electromagnetic wave can easily be propagated in a curvilinear form, an advantage can be obtained in that a millimeter wave integrated circuit can be downsized, and high flexibility in circuit design can be obtained.
As the material of the dielectric strip 12 of the NRD guide S1, a resin material having a dielectric constant of from 2 to 4, such as Teflon and polystyrene, has been conventionally used owing to its easiness in processing.
However, the dielectric constants of alumina ceramics and forsterite ceramics used in the conventional resonator are about 10 and about 7, respectively, and therefore, a material having a lower dielectric constant is being demanded associated with spreading of a dielectric resonator for a high frequency band in recent years.
On the other hand, porcelain, such as glass ceramics, which is generally used as a low dielectric constant material, has a small dielectric constant of about from 4 to 6 but has a Q value of about 1,000 at 10 GHz, and therefore, a low dielectric constant material having a higher Q value is being demanded associated with spreading of a dielectric resonator for a high frequency band in recent years.
Furthermore, since alumina ceramics, which is mainly used as the dielectric board 3 of the dielectric resonator, has a relatively high dielectric constant of about 10, it involves such a problem that when a strip line of a high impedance is to be formed, the line width is too decreased to about 1 xcexcm or less to cause breakage, and fluctuation in the relative line width is increased, whereby the defective fraction is increased when a microwave integrated circuit is fabricated by using the dielectric resonator.
This is because the impedance of the strip line in the dielectric board 3 is inversely proportional to the dielectric constant thereof and the width of the strip line, respectively, assuming that the thickness of the dielectric board 3 is constant. Therefore, the impedance can be increased by using a material having a lower dielectric constant instead of reduction in the width of the strip line. Thus, a material having a low dielectric constant is being demanded.
In order to solve the problems, the inventors have proposed a dielectric porcelain composition for a high frequency and a dielectric resonator, which comprise a complex oxide containing Mg, Al and Si as metallic elements, in which the molar composition of the respective metallic elements in the oxide xMgOxc2x7yAl2O3xc2x7zSiO2 satisfies 10xe2x89xa6xxe2x89xa640, 10xe2x89xa6yxe2x89xa640, 20xe2x89xa6zxe2x89xa680, and x+y+z=100, the dielectric constant is 6 or less, and the Q value of 2,000 or more at a measuring frequency of 10 GHz (Japanese Unexamined Patent Publication JP-A 9-48661 (1997)).
The dielectric porcelain composition for high frequencies is of excellent properties as having a dielectric constant lower than those of alumina ceramics and forsterite ceramics, and a Q value higher than that of glass ceramics. However, a dielectric porcelain composition exhibiting a high Q value at a higher frequency is still demanded.
When the conventional NRD guide is constituted by a dielectric strip using a dielectric material comprising a resin material, such as Teflon and polystyrene, there is a problem that the curvature loss at a curved part of the dielectric strip and the loss at a junction of the dielectric strips are large. Therefore, a sharp curved part cannot be formed in the dielectric strip, which brings about, as a result, such a problem that the NRD guide has a large size. In the case where a loose curved part is formed in the dielectric strip, it is necessary that the curvature of the curved part be precisely determined to suppress the high frequency signal loss.
Furthermore, the frequency range that can be used under the condition that the curvature loss is small is 1 to 2 GHz in the vicinity of 60 GHz, which is insufficient. This is because in the case where the NRD guide is constituted with a dielectric material having a dielectric constant of from 2 to 4, the distance between the LSM mode and the LSE mode is too close as about 3 GHz, and thus a part of the electromagnetic wave in the LSM mode is converted to the LSE mode. That is, with respect to the diffusion characteristics of the LSM mode and the LSE mode, the diffusion curves of the two modes is separated from each other by only about 3 GHz at B/B0=0 (B represents a propagation constant of a high frequency signal in a dielectric strip, and B0 represents a propagation constant of a high frequency signal in vacuum), which causes the conversion of a part of the electromagnetic wave in the LSM mode to the LSE mode. There has been a product using ceramics having a dielectric constant of about 10, such as alumina, as the material of the dielectric strip, but in order to use it at a high frequency of 50 GHz of higher, it is necessary that the width of the dielectric strip is extremely narrow, and it is not practical on processability and workability of fabrication, i.e., on productivity.
Furthermore, the cross section of the dielectric strip becomes smaller when the frequency becomes higher. For example, in the case where a dielectric strip having a cross sectional size of about 1 mmxc3x972 mm and a length of about 10 mm is formed with porcelain and arranged, a problem occurs in that the dielectric strip is extremely liable to broken on handling upon production. Moreover, it is necessary to retain the dielectric strip by a pair of parallel flat conductive bodies, but a problem occurs in that the dielectric strip is broken upon fastening with the parallel flat conductive bodies.
An object of the invention is to provide a dielectric porcelain composition in which phase conversion of xcex1 phase to xcex2 phase of a cordierite phase as a primary crystalline phase is not large, i.e., the phase conversion to xcex2 phase does not sufficiently proceed, so as to have a dielectric constant of from 4.5 to 6 and a Q value of 1,000 or more at 60 GHz. Another object of the invention is to increase impedance in a dielectric resonator by using a dielectric board material of low dielectric constant comprising the dielectric porcelain composition, instead of by reducing the width of a strip line on a dielectric board. Still another object of the invention is to provide an NRD guide using a dielectric strip with small conversion from LSM mode to LSE mode of electromagnetic waves, comprising the dielectric porcelain composition and having a curved part, so as to broaden the usable frequency range even when the sharp curved part is used, whereby a millimeter wave integrated circuit can be downsized with high workability and high freedom on design.
The invention provides a dielectric porcelain composition comprising, as a principal component, a complex oxide having a molar composition xMgOxc2x7yAl2O3xc2x7zSiO2 (wherein 10xe2x89xa6xxe2x89xa640, 10xe2x89xa6yxe2x89xa640, 20xe2x89xa6zxe2x89xa680, and x+y+z=100), a primary crystalline phase of the complex oxide being a 2MgOxc2x72Al2O3xc2x75SiO2 phase, and a ratio of a (241) peak intensity xcex2p(241) and a (222) peak intensity xcex2p(222) of X-ray diffraction of a xcex2 phase of the primary crystalline phase being 0.8xe2x89xa6xcex2p(241)/xcex2p(222)xe2x89xa61.3.
According to the invention, the principal component of the dielectric porcelain composition is the complex oxide having a molar composition of the specific range, and the primary crystalline phase thereof is the cordierite (2MgOxc2x72Al2O3xc2x75SiO2) phase of the specific phase conversion state, whereby such characteristics can be obtained that the dielectric constant is from 4.5 to 6.0, and the Q value is 1,000 or more at 60 GHz.
In the invention it is possible that the dielectric porcelain composition contains 0.1 part by weight or less of an alkali metal element in terms of an oxide per 100 parts by weight of the complex oxide.
According to the invention, the rate of phase conversion of the xcex1 phase to the xcex2 phase of the cordierite (2MgOxc2x72Al2O3xc2x75SiO2) phase as the primary crystalline phase is made slow by decreasing the content of an alkali metal element, so as to put the cordierite phase to the xcex2 phase which is in a state closer to the xcex1 phase, whereby a dielectric porcelain composition exhibiting high Q value can be stably obtained.
In the invention it is preferable that the alkali metal element is potassium.
According to the invention, by making small the content of potassium, which particularly makes faster the rate of phase conversion of the xcex1 phase to the xcex2 phase of the cordierite (2MgO.2Al2O3.5SiO2) phase, the cordierite phase can be easily put to the xcex2 phase which is in a state closer to the xcex1 phase, whereby a dielectric porcelain composition exhibiting high Q value can be stably obtained.
In the invention it is preferable that the dielectric porcelain composition contains 0.1 to 15 parts by weight of a rare earth element in terms of an oxide per 100 parts by weight of the complex oxide.
According to the invention, since the dielectric porcelain composition contains a certain amount of a rare earth element, the sintering conditions of the dielectric porcelain composition can be improved without largely deteriorating the characteristics such as Q value. That is, in order to obtain such characteristics that the dielectric constant is from 4.5 to 6.0, and the Q value is 1,000 or more at a measuring frequency of 60 GHz, the sintering temperature range can be broadened to about 100xc2x0 C., which has been conventionally controlled with a width of about 10xc2x0 C., whereby the production thereof becomes easy to remarkably improve the mass productivity.
In the invention it is preferable that the rare earth element is at least one selected from the group consisting of Tb, Dy, Ho, Er, Yb and Lu.
According to the invention, sintering can be conducted at a low temperature particularly without deterioration of Q value, whereby the production of the dielectric porcelain composition becomes easy to remarkably improve the mass productivity.
The invention provides a dielectric resonator comprising:
a dielectric board;
a dielectric supporting member; and
a dielectric porcelain for resonance having a higher dielectric constant than that of the supporting member, the dielectric porcelain provided on the dielectric board via the dielectric supporting member,
the dielectric board and/or the dielectric supporting member comprising a dielectric porcelain composition which comprises, as a principal component, a complex oxide having a molar composition xMgOxc2x7yAl2O3xc2x7zSiO2 (wherein 10xe2x89xa6xxe2x89xa640, 10xe2x89xa6yxe2x89xa640, 20xe2x89xa6zxe2x89xa680, and x+y+z=100), a primary crystalline phase of the complex oxide being a 2MgOxc2x72Al2O3xc2x75SiO2 phase, and a ratio of a (241) peak intensity xcex2p(241) and a (222) peak intensity xcex2p(222) of X-ray diffraction of a xcex2 phase of the primary crystalline phase being 0.8xe2x89xa6xcex2p(241)/xcex2p(222)xe2x89xa61.3.
According to the invention, since the dielectric supporting member is of low dielectric constant and of large Q value, leakage of the electric field of the dielectric porcelain through the dielectric supporting member can be controlled, whereby a resonance system of high unloaded Q can be constituted. Furthermore, since the dielectric board is of low dielectric constant, the impedance can be increased without reduction in the line width of the strip line. According to the constitution, a high frequency circuit such as a microwave integrated circuit, can be produced with high reliability.
In the invention it is preferable that the dielectric porcelain composition contains 0.1 part by weight or less of an alkali metal element in terms of an oxide per 100 parts by weight of the complex oxide.
According to the invention, the dielectric board and/or the dielectric supporting member exhibiting high Q value can be stably obtained by decreasing the content of an alkali metal element in the dielectric porcelain composition, whereby a high frequency circuit such as a microwave integrated circuit can be produced with high reliability.
In the invention it is preferable that the alkali metal element is potassium.
According to the invention, the dielectric porcelain composition exhibiting high Q value can be stably obtained by decreasing the content of potassium in the dielectric porcelain composition, whereby a high frequency circuit such as a microwave integrated circuit can be produced with high reliability.
In the invention it is preferable that the dielectric porcelain composition contains 0.1 to 15 parts by weight of a rare earth element in terms of an oxide per 100 parts by weight of the complex oxide.
According to the invention, the sintering conditions of the dielectric porcelain composition can be improved without largely deteriorating the characteristics thereof, such as the Q value, by containing a certain amount of a rare earth element, whereby the production thereof becomes easy to remarkably improve the mass productivity.
In the invention it is preferable that the rare earth element is at least one selected from the group consisting of Tb, Dy, Ho, Er, Yb and Lu.
According to the invention, sintering can conducted at a low temperature particularly without deterioration of the Q value, by containing the certain rare earth element, whereby the production of the dielectric porcelain composition becomes easy to remarkably improve the mass productivity.
The invention also provides a nonradiative dielectric strip comprising:
a pair of parallel flat conductive bodies arranged with a distance of xc2xd or less of a wavelength of a high frequency signal; and
a dielectric strip disposed between the parallel flat conductive bodies, for transmitting the high frequency signal,
the dielectric strip comprising a dielectric porcelain composition which comprises, as a principal component, a complex oxide having a molar composition xMgOxc2x7yAl2O3xc2x7zSiO2 (wherein 10xe2x89xa6xxe2x89xa640, 10xe2x89xa6yxe2x89xa640, 20xe2x89xa6zxe2x89xa680, and x+y+z=100), a primary crystalline phase of the complex oxide being a 2MgOxc2x72Al2O3xc2x75SiO2 phase, and a ratio of a (241) peak intensity xcex2p(241) and a (222) peak intensity xcex2p(222) of X-ray diffraction of a xcex2 phase of the primary crystalline phase being 0.8xe2x89xa6xcex2p(241)/xcex2p(222)xe2x89xa61.3.
In the invention it is preferable that the dielectric porcelain composition contains 0.1 part by weight or less of an alkali metal element in terms of an oxide per 100 parts by weight of the complex oxide.
In the invention it is preferable that the alkali metal element is potassium.
In the invention it is preferable that the dielectric porcelain composition contains 0.1 to 15 parts by weight of a rare earth element in terms of an oxide per 100 parts by weight of the complex oxide.
In the invention it is preferable that the rare earth element is at least one selected from the group consisting of Tb, Dy, Ho, Er, Yb and Lu.
In the invention it is preferable that a dielectric constant of the dielectric porcelain composition is from 4.5 to 6.
According to the invention, the dielectric strip for transmitting a high frequency signal comprising the dielectric porcelain composition having the specified characteristics is provided between the pair of parallel flat conductive bodies arranged with a distance of xc2xd or less of a wavelength of a high frequency signal, and thus the dielectric constant of the dielectric strip becomes about from 4.5 to 6.0, which is higher than the conventional resin material, such as Teflon, but lower than alumina ceramics, whereby the loss caused by conversion of the electromagnetic wave in the LSM mode to the LSE mode can be decreased. When a dielectric porcelain having a Q value of 1,000 or more at a using frequency of 60 GHz is used, the transmission loss can be small, and the width of the dielectric strip is not necessarily extremely narrow to easily form the dielectric strip, whereby the dielectric strip can be produce at a low cost with high accuracy. Furthermore, since the dielectric constant of the dielectric strip is higher than the resin material, such as Teflon, the influence of the resin material can be suppressed even when a supporting jig and a circuit board of the dielectric strip are formed with the resin material. Accordingly, an NRD guide of a small size and a low cost with a high degree of freedom on production can be constituted.